1. Field of the Invention
The present invention generally relates to a digital micro mirror device (DMD) and a single-panel color projector using the digital micro mirror device.
2. Description of the Related Art
In the field of color projectors, a projector that displays a brighter large-screen image is desirable. An example of such a projector is a conventional three-panel projector using three light valves including liquid crystal panels. This projector has been popular because it is easy to install, has good portability, and has high intensity. However, the cost of light valves is high, and thus the cost of a device (e.g., the projector) using three light valves has been very high. Further, the optical system is also complicated, and thus the device is oversized.
Alternatively, in a color sequential display method, one light valve having a high response speed is used and light in the three primary colors is successively projected at high speed by a rotating color disk or the like. In this approach, a field image of each color is successfully displayed providing a seemingly full-color frame display to the viewer. This method allows for a device that is small, lightweight and inexpensive because only one light valve is used and the optical system is simple.
The liquid crystal panel, of a transparent or reflective type, used in a three-panel liquid crystal projector is not capable of a response speed high enough for use in the color sequential display method. Therefore, in the color sequential display method, a light valve, such as a digital micro mirror device (DMD) or reflective-type ferroelectric liquid crystal panel formed on crystalline silicon, is used. Since these are binary-type devices (e.g., having only the two states of ON/OFF), grayscales are achieved by controlling the ON/OFF duty with a Pulse Width Modulation (PWM) control, for example. However, PWM has low intensity since ⅔ of white light from a light source is lost when using a color disk.
In the color sequential display method using one light valve, if two or all three primary colors separated from white light can be effectively used, a high-intensity and inexpensive projector can be provided.
U.S. Pat. No. 5,410,370 and U.S. Pat. No. 5,528,318 describe color sequential display methods using a rotating prism. The prism separates a white light source into color bands of red, green and blue and moves the color bands, to scan a light valve. Since a liquid crystal panel used for a three-panel liquid crystal projector is incapable of a response speed necessary for a color successive display method, a light valve such as a DMD or reflective-type ferroelectric liquid crystal panel formed on crystalline silicon should be used, and the assignment of intensity levels should be implemented by PWM.
However, because of the necessity of separating the color bands, this method makes the width of the bands narrower and a time to illuminate the light valve with the color bands shorter. Therefore, it is impossible to acquire sufficient grayscales using PWM. In addition, a very complicated control of PWM is necessary since a passing speed of the color bands changes in a non-linear manner because rotation of the prism and the timing for switching colors of the color band is different for each pixel line.
A high-intensity single-panel projector is possible by replacing a rotating color disk with a double rotating dichroic mirror disk, thereby separating a white light beam from the white light source into three light beams. The three light beams, each of which is changing color in the order of green-blue-red, red-green-blue, blue-red-green, and each light beam incident to a third of the area of a light valve, such as one DMD, effectively use all the light separated into the three primary colors. Since this method has the same illumination time as a conventional single panel method, sufficient grayscales are acquired by PWM, and colors of incident light change simultaneously. Thus, control of PWM becomes easier.
However, this method causes a phenomenon in which the three light beams overlap adjacent areas, and a problem arises in that the overlap area does not display the desired color. Further, if a black mask or the like is placed among the three areas in order to prevent overlapping, the three areas cannot be displayed continuously as one image.
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional digital micro mirror devices, the present invention has been devised, and it is, therefore, an object of the present invention to provide a digital micro mirror device where at least two of the three primary colors can be effectively used by illuminating a light beam separated into the three primary colors to a third of an area of a light valve and reflecting it therefrom.
Further, it is an object of the present invention that even light beams overlapping adjacent areas will not adversely affect a projected image.
It is a further object of the invention to provide, in a color sequential display, using one digital micro mirror device, a single-panel color projector that makes at least two of the three primary colors obtained from white light to be used effectively, thereby providing a low-cost device having high intensity and which securely displays colors and controls a PWM for displaying grayscales.
In a first aspect of the present invention, a digital micro mirror device includes an array of micro mirrors on a reflection surface, the reflection surface being divided into two or more areas, the direction of an axis about which each mirror rotates being different in an adjacent area and two or more light beams being illuminated to the corresponding areas respectively and reflecting them therefrom.
In a second aspect of the present invention, a single-panel color projector includes a white light source, a color separator for separating a white light from the white light source into two or more light beams so that the three primary light colors appear successively and the same color does not appear at the same time as another, a digital micro mirror device having an array of micro mirrors on its reflection surface, the reflection surface being divided into two or more areas, and a direction in which a mirror rotates on an axis being different in adjacent areas among the two or more areas, and two or more beams being illuminated into the corresponding areas respectively and being reflected therefrom, an illumination light illuminating each light beam from the color separator so that the incident light corresponds to a rotating axis direction of each area thereof, and a projector for collecting the light reflected in the predetermined direction from the digital micro mirror device, the projector for projecting the collected light.
With the unique and unobvious aspects of the present invention, two or all three primary colors can be separated from white light and effectively used by illuminating each light beam into different areas and reflecting it therefrom, without illumination light from overlapping adjacent areas adversely affecting a projected image.
The present disclosure relates to subject matter contained in Japanese Patent Application 11-143194, filed May 24, 1999, which is expressly incorporated herein by reference in its entirety.